Toner is a fine, polymer-based powder which is used to form texts and images on the printed paper by electrophotographic technology. It is generally electrically charged or possessing magnetic properties. It is widely used in laser printers, photocopiers and fax devices, which are based on electrophotographic technology invented more than 30 years ago. Toner starts off as a powder, and passes through these electrophotographic machines being heated to a fluid and ends up as a solid as it is cooled down and bonded to the printed paper.
An electrophotographic process generally involves steps of utilizing a photoconductive material, forming an electrostatic latent image on a photosensitive member by using various means, exposing light onto the document with texts or images, followed by developing the latent texts or images with toners to produce visible texts or images, then transferring the toners onto a transferring material such as paper and fixing the toners onto the transfer material by using heat, pressure or the like to provide a copied article.
We can illustrate the usage of toners via the operation of a photocopy machine which uses electric charges to transfer an image to a plain piece of paper. The document to be copied is placed face down on the platen and illuminated by a lamp. Its image is directed to an electrical charged metal electrostatic drum by light reflection using mirrors. Where light strikes the drum, the white areas of the document become conductive and therefore discharge to ground, but that dark areas remain charged. Opposite charged toner particles are applied onto the drum and these particles stick only to the charged areas. The image on the drum is then transferred to a piece of paper. A heater is used to seal the toner by melting it onto the paper.
The toner resins will give toner its overall physical ability to be first a fine powder, then melt at a suitable temperature, then form a permanent plastic solid capable of bonding to the paper. The majority of toners are manufactured using a melt mixing process. The color in the toner comes from the pigment blended into the polymer particles while they are being made.
The conventional toner is made by compounding the ingredients, such as resins, pigment, magnetic iron oxides, waxes and charge control agents by melting and blending the ingredients to form a paste. This mixture is then cooled by extruding onto a cooling belt into thin plate. The raw toner is then pulverized and ground into a fine powder within a controlled particle size range by jet mills or air-swept hammer mills. This process resulted in toner granules of various sizes and jagged shapes when viewed under a microscope.
The over-size and under-size toner particles are sieved out in a 1 to 3 pass process. The pulverized powder is then blended with additives to adjust flow and electrostatic properties. This final blending is critical and difficult to control, especially when the additives particle size is much different from the required toner particle size.
Today, various companies are using chemical process to produce toner particles so as to get a finer print. As a result, toner particles of more uniform sizes and shapes are produced. The finer and more uniform shapes enable more accurate color reproduction and more efficient toner use.
Currently there are two main types of conventional toner resins: (i) styrene-acrylate copolymer produced by radical initiated addition polymerization, and (ii) polyester resin by stepwise condensation polymerization. The raw materials involved are petroleum-based chemicals. While styrene-acrylate copolymers are made from monomers such as styrene, butyl acrylate and acrylic acid, which are derived from petrochemicals; the polyester toner resins are also synthesized from petrochemicals such as ethylene glycol, 1,4-butandiol or other polyol in combination with polyfuctional acids such as phthalic anhydride, adipic acid, isophthalic acid, and sebacic acid.
Toner formulations vary from manufacturer to manufacturer and different toners are produced to suit different machines. The toner resins described in the prior arts include a wide range of variation in their producing method and product quality.
There is a dry process color toner described by the Japanese Pat. No. JP61112160 to Takayama, issued in 1986. This yellow toner is obtained by incorporating an azomethine oil-soluble dye into a synthetic resin, natural resin, rubber or wax. This incorporation prevents the toner from being opaque by the secondary aggregate of a color material as well as from having a hiding effect in the stage of superposing multiple colors and to eliminate the deterioration of electrostatic chargeability.
Another Japanese Pat. No. JP9034174 to Ishida, issued in 1997, also discusses an invention relating to the toner for electrostatic-charge image development, its manufacture approach and the image formation approach for developing an electrostatic latent image. The main component of this toner is a polyester binder resin, which is incorporated with coloring agent and release agent. The advantages of this toner is capable of providing a good fixing property and blocking resistance as well as controlling the dielectric loss tangent to a specific value.
U.S. Pat. No. US2007020549 to Koyama, published in 2007 relates to a method of manufacturing a polymerized toner which is a composites made from a polyester resin and a styrene-acrylate copolymer resin. This toner has an excellent fixability at low temperature in an image forming process, fine-line reproducibility and easy productivity. The invention also discusses a product of toner manufactured by said method, and an image forming method.
Another U.S. Pat. No. US2007/0026336A1 to Katsuhisa, published in 2007, describes an invention of a toner including a binder resin and a colorant which also enables low temperature fixation irrespective of the constitution of a fixing unit. The toner also stably provides high image quality even when the toner is used at a high humidity or a low humidity.
Still another U.S. Pat. No. US20070072107A1 to Cheong, published in 2007 relates to a different method of synthesizing a toner having a core formed of a polyester resin and a colorant, wherein the core is encapsulated with a macromonomer and/or a reactive emulsifying agent as well as a polymerizable monomer resin.
Since toner resin is being applied in various types of electrophotographic devices in recent years, there has been higher demand of toner resins. Seeing the existing toner resins are mostly made from petrochemicals which are derived from the non-renewable resources, which are non-sustainable, the synthesis of polyester toner resins with high content of natural material is desirable. More specifically, the synthesis of palm oil-based polyester resins, which could be easily converted to toner resins through a controlled crosslinking process, is an environmental friendly approach as compared to the conventional resins made from petrochemicals.